Seal compositions, methods, and structures for planar solid oxide fuel cells
View Patent ↗A seal composition includes a first alkaline earth metal oxide, a second alkaline earth metal oxide which is different from the first alkaline earth metal oxide, aluminum oxide, and silica in an amount such that molar percent of silica in the composition is at least five molar percent greater than two times a combined molar percent of the first alkaline earth metal oxide and the second alkaline earth metal oxide. The composition is substantially free of boron oxide and phosphorus oxide. The seal composition forms a glass ceramic seal which includes silica containing glass cores located in a crystalline matrix comprising barium aluminosilicate, and calcium aluminosilicate crystals located in the glass cores.
1. A seal composition comprising:
a first alkaline earth metal oxide;
a second alkaline earth metal oxide, wherein the second alkaline earth metal oxide is different from the first alkaline earth metal oxide;
aluminum oxide; and
silica in an amount such that molar percent of silica in the composition is at least five molar percent greater than two times a combined molar percent of the first alkaline earth metal oxide and the second alkaline earth metal oxide;
wherein the composition is substantially free of boron oxide and phosphorus oxide.
2. The composition of claim 1 , wherein the composition comprises:
between about 5 mole percent and about 25 mole percent of the first alkaline earth metal oxide;
between about 2 mole percent and about 25 mole percent of the second alkaline earth metal oxide;
between about 5 mole percent and about 15 mole percent of the aluminum oxide; and
between about 45 mole percent and about 65 mole percent of the silica.
3. The composition of claim 2 , wherein the first alkaline earth metal oxide comprises at least 80 molar percent calcium oxide and the second alkaline earth metal oxide comprises at least 80 molar percent barium oxide.
4. The composition of claim 2 , wherein a molar ratio of the first alkaline earth metal oxide to the second alkaline earth metal oxide in the composition is between about 5:1 and about 1:5.
5. The composition of claim 2 , wherein the composition comprises zero to about 0.5 molar percent of boron oxide and phosphorus oxide.
6. The composition of claim 5 , wherein the composition consists of barium oxide, calcium oxide, alumina and silica and the composition is substantially free of other glass formers and easily reducible species.
7. The composition of claim 6 , wherein the composition comprises zero to about 0.5 molar percent of arsenic oxide, lead oxide or zinc oxide.
8. The composition of claim 2 , wherein the composition further comprises less than 5 molar percent of at least one of a fluxing agent or a bulk nucleation agent.
9. The composition of claim 1 , wherein the composition is in glass powder form.
10. The composition of claim 1 , wherein the composition comprises a glass ceramic seal located in a fuel cell stack.